1. Field of the Invention
The present invention relates to preamble noise cancellation circuits, and more particularly, to a preamble noise cancellation circuit that can more accurately perform signal processing using a preamble by cancelling noise included in the preamble of a communication signal (hereinafter, referred to as “preamble noise”).
2. Description of the Related Art
In general, with the popularization of mobile digital broadcasting, digital multimedia broadcasting (DMB), digital video broadcasting-handheld (DVB-H), and media-forward link only (media-FLO) receivers have been increasingly provided in cellular phones, navigations, and notebook computers.
However, as individual digital broadcasting systems within general IT equipment have been complicated, various system signals, generated from the general IT equipment, serve as interference signals with respect to an added digital broadcasting system. This causes deterioration in communication quality of the digital broadcasting system. However, a specific solution to overcome the deterioration has not been proposed yet.
The research and development of a technique that removes an interference signal having a very high level has now been conducted.
Currently, examples of a communication system using industrial, scientific and medical (ISM) bands may include applications such as a wireless LAN (WLAN), Bluetooth, and Zigbee. When these communication systems are used by individual users within a predetermined space or operate in a notebook computer or a desktop computer of a single user at the same time, transmission/reception frequencies used in the respective communication systems may be close or overlap. This causes a significant reduction in quality of each of the communication systems.
For example, when the WLAN, the Bluetooth, and the Zigbee systems exist together and are in use within a predetermined space, the WLAN may be used for Internet access and data transmission, a Bluetooth device may be used to perform voice and audio communication and provide an interface to PC peripheral devices.
Further, while devices and equipment are monitored and controlled using the Zigbee, a large amount of data can be transmitted and received using the WLAN. For example, in transmission and reception frequency channels of the WLAN and the Zigbee using the ISM bands at the same time, at least four Zigbee communication channels overlap with one WLAN communication channel. When different devices sharing the ISM bands operate at the same time at a predetermined space, the communication frequencies used by the respective systems may overlap each other or be located within an adjacent frequency band. As a result, the communication signals from other systems serve as interference to each other, which may cause a reduction in communication quality of all of the corresponding systems or make communication impossible.
In order for a communication terminal to restore desired data from the received signal, synchronization between a transmission system and a reception system needs to be a top priority. To this end, a transmission terminal adds a preamble having a predefined format to ensure synchronization of a reception terminal, which is followed by a frame of signal data to be transmitted, and transmits the preamble. The reception terminal checks the preamble first to acquire the synchronization, and can restore desired signal data at a predetermined position. In a case of a received signal injected into an antenna of the receiver through a transmission medium where noise is present, if the injected interference signal has a signal level lower than SNR that the reception system asks for, the receiver can stably detect the preamble to acquire synchronization, and then can restore desired data by performing data processing.
However, when the injected interference signal has a signal level greater than the SNR that the receiver asks for, it may be impossible for the receiver to detect the preamble. Therefore, the receiver cannot acquire synchronization necessary for restoring data, and thus cannot perform data processing. As a result, the receiver cannot receive the data. Even when an error occurs in a data frame field during the transmission, most of the communication systems can restore an original signal by using various coding schemes to overcome the error. However, when the synchronization is not acquired in the preamble field in an early stage of the reception, cyclic redundancy checking (CRC) becomes of no use.